Recently, electrophotographic image formation using electrostatic image developing toners (hereinafter, also denoted simply as toners) has been applicable to full-color prints as well as monochromatic prints as typified in conventional documentation. Such full-color image forming apparatuses, which can make printed sheets as required on demand without making printing plates, as in conventional printing, have been employed mainly for short-run printing in which orders for small number of print is often received, as set forth in, for example, JP-A No. 2005-157314 (hereinafter, the term JP-A refers to Japanese Patent Application Publication).
When making full-color prints used for catalogues or printed advertisements by using toners, color reproduction of images faithful to the original is required in the toners. In full-color image formation, yellow, magenta and cyan toner images are superimposed to reproduce a targeted color image and superior color reproducibility of these toners is a basic requirement to realize faithful color reproduction.
Accordingly, there have been studied colorants including various metal complex dyes to achieve enhanced color reproducibility of color toners.
Typical examples of colorants for color toners include copper phthalocyanine pigments. Toners using copper phthalocyanine pigments are generally used and exhibit superior lightfastness, but result in images with reflection spectrum having a higher base-line on the longer wavelength side and tend to form seemingly color-contaminated images. Accordingly, such pigments have been regarded as unsuitable for image formation demanding higher color reproduction, as typified in prints of company logos.
There were attempted efforts at improvement of copper phthalocyanine pigments to develop a toner causing no color contamination, as set forth in, for example, JP-A No. 5-239368, but these attempts have not led to sufficient reduction of color contamination.
Toners using pigments such as copper phthalocyanine pigments exhibited versatility in that image quality at a level of images formed by printing inks was achieved, but having difficulty in displaying a hue angle suitable for color reproduction of a photographic image. Instead of using copper phthalocyanine pigments, there was studied a toner containing a colorant capable of displaying a hue angle suited for color reproduction of photographic images, as set forth in JP-A Nos. 5-239368 and 2006-63171.